High pressure NMR Stucy of Unusual Magnetism and characteristic Superconductivity apperaing in Uru2Si2 and UPt3

本课题的主要目的有两个：一是获得高压下URu_2Si_2反铁磁区超导能隙的信息;二是利用Pt NMR研究高压下自旋涨落被强烈抑制的UPt_3中异常小磁矩的起源。由于超导转变温度从1.5K开始随压力的增加而急剧下降，为了得到能隙的详细结构，我们尝试用稀释制冷机测量了20 ~ 30 mK范围内核自旋弛豫速率随温度的变化。然而，在我们的稀释参考中获得的最低温度约为250 mK，因为有限的冷却功率和大的高压池（直径20 mm，高度90 mm）。因此，我们必须设计改进的高压池，以进一步在低温下进行NMR/NQR测量。幸运的是，我们可以在高压电池中的URu_2Si_2的反铁磁区找到较弱的~（29）Si NMR信号。高压硅核磁共振表明，高压下得到的反铁磁区磁性均匀，磁矩为0.3 μB。其次，我们试图购买用于高压NMR测量的富集的195 Pt，因为如果存在的话，在高压池中可以预期只有非常弱的Pt信号。然而，法国和美国产品的富集铂标称（化学）纯度为99.0%至99.3%，尽管富集度为99.8%。为了使样品的质量与以前报道的样品几乎相同，至少需要大于99.9%的化学纯度。因此，我们放弃了利用富集铂制备高质量UPt 3。(290字）

The purpose of this subject is the following two issues : one is to get the information on the superconducting energy gap appearing in the antiferromagnetic region of URu2Si2 under high pressure) the other is to get the origin on unusually small magnetic moment by Pt NMR in UPt3, where spin fluctuations are strongly suppressed by high pressure. For the purpose of getting the detailed structure of gap, we tried to measure the temperature dependence of nuclear spin relaxation rate down to 20 thru 30mK by a dilution refrigerator, because the superconducting transition temperature decreases drastically from 1.5 K with increasing pressure. However, the lowest temperature obtained in our dilution ref. is about 250 mK because of limited cooling power and a big high pressure cell (20mm in a diameter and 90mm in height). So we have to design the improved high pressure cell for the further NMR/NQR measurement at low temperatures. Fortunately, we could find weak 29Si NMR signal in the antiferromagnetic region of URu2Si2 attached in high pressure cell. Moreover, high pressure Si NMR revealed that the antiferromagnetic region obtained by applying high pressure is magnetically quite uniform with magnetic moment, of 0.3 μB. Secondly, we tried to purchase enriched 195 Pt for high pressure NMR measurement, because just a very weak Pt signal could be expected in the high pressure cell, if exists. The nominal (chemical) purity in enriched Pt was, however, 99.0 % thru 99.3 % for French and US products, though the enrichments were 99.8%. In order to have the sample of almost the same quality compared with the previously reported samples, more than 99.9 % in chemical purity is necessary at least. So we gave up to prepare UPt3 of high quality using enriched Pt. (290 words)